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Thread: Leaking port fuel tank on landing and left rudder slip

  1. #121

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    Each time I drained the tank and waited for spring to repair. The next spring no leak. Knock on wood, no leak so far this October.
    .
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  2. #122

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    Quote Originally Posted by don d View Post
    Each time I drained the tank and waited for spring to repair. The next spring no leak. Knock on wood, no leak so far this October.
    .
    Sounds like either the tank fixing fairies, or something that blossoms when the fuel is away, is filling the hole?!! Certainly cheaper than sending it off to the tank shop


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  3. #123

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    Test flew today and VERY happy to report that all the fixes and improvements worked GREAT!!!! However, there's still a slight trickle of fuel down the wing in a prolonged/steep left rudder sideslip BUT NOTHING like there was before

    I'm not panicking, as pretty much everyone says this is "normal" with a vented cap, however I would like to reduce this further. A friend with a PA-18 has soldered a forward facing pipe onto the vent, to keep some pressure in the vent and avoid the fuel spill, has anyone done this with caps like mine, which are chrome and with a locking vertical spine down the middle, which a slot in the hinged catch on the tank cover slots over? There seems to be little vents in the centre of the cap, on each side of the spine

  4. #124
    cubpilot2's Avatar
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    Several cap options from Atlee Dodge

    http://www.fadodge.com/category/piper/fuel-systems/
    Ed
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  5. #125

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    Leaking port fuel tank on landing and left rudder slip

    Quote Originally Posted by cubpilot2 View Post
    Several cap options from Atlee Dodge

    http://www.fadodge.com/category/piper/fuel-systems/
    Thanks CubPilot2!!! Mine are the Piper Vented Caps! and the 180hp one looks like the one my PA-18 friend described, what’s the significance of the 180hp on these caps? Do they also get used on other engines?


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  6. #126

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    They add positive pressure to the tank while flying to meet the CAR 3 max fuel flow requirements for the 180 HP.
    DENNY

  7. #127
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    [QUOTE=Philly5G;730432]Thanks CubPilot2!!! Mine are the Piper Vented Caps! and the 180hp one looks like the one my PA-18 friend described, what’s the significance of the 180hp on these caps? Do they also get used on other engines?


    Typical with some 180 conversion STC’s
    Evedently meant to ensure fuel flow with slight pressurization of system from ram air.

    I dont buy that your fuel leak is “normal”. Keep checking. If it’s the caps, borrow your friends and test them or swap sides with your own. They should grip firmly with good gaskets.
    Ed
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  8. #128

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    [QUOTE=cubpilot2;730446]
    Quote Originally Posted by Philly5G View Post
    Thanks CubPilot2!!! Mine are the Piper Vented Caps! and the 180hp one looks like the one my PA-18 friend described, what’s the significance of the 180hp on these caps? Do they also get used on other engines?


    Typical with some 180 conversion STC’s
    Evedently meant to ensure fuel flow with slight pressurization of system from ram air.

    I dont buy that your fuel leak is “normal”. Keep checking. If it’s the caps, borrow your friends and test them or swap sides with your own. They should grip firmly with good gaskets.
    The tank has been removed and repaired for leaks. When I confidence tested it myself before refitting with a couple of gallons of fuel by sloshing around all was fine, until I turned it upside down and fuel came out of the cap vent holes, as you’d probably expect!! The gaskets are new and fit securely.

    Given the long thin design of the tanks, if they’re more than half full any kind of bank angle is going to get the fuel level moving towards the cap and if it gets to the caps, what’s to stop it dribbling out of the vents as it does when the tank’s inverted?


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  9. #129
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    [QUOTE=Philly5G;730460]
    Quote Originally Posted by cubpilot2 View Post

    When I confidence tested it myself before refitting with a couple of gallons of fuel by sloshing around all was fine, until I turned it upside down and fuel came out of the cap vent holes, as you’d probably expect!!
    A proper test for leaks would be to apply 3 psiof air pressure to the tank. Then brush soapy water over all of the seams looking for bubbles. Sloshing around as you did won't necessarily show pin hole leaks.
    N1PA
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  10. #130

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    That’s what the tank repair shop did when they tested it and soldered the leaks I just sloshed a bit of fuel around in it when I got it back, partly to make sure any little bits that may have been in it were washed out and for a bit of a confidence test. All good except for the upside down bit when the fuel came out of the vents, but not the side of the cap


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  11. #131
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    Fuel might get out vents in a turn but would
    would be sucked into the slip stream, not run down
    the wing.

    Can you you post a photo of your caps.
    The vent hole described sounds a bit strange.
    Ed
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  12. #132

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    Will do on the cap pics!

    Good point on the fuel being blown into the slipstream, although this now only happens in the sideslip. I might mount my GoPro looking at the cap and go do some more sideslips


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  13. #133
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    Philly,

    Youre forgetting that while in flight, your engine should be running, thus imposing a (slight) negative pressure on the tanks, which is being relieved via the vented caps. Holding a tank upside down with fuel in it prior to installation is a somewhat meaningless excersize.

    MTV
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  14. #134

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    Quote Originally Posted by mvivion View Post
    Philly,

    Youre forgetting that while in flight, your engine should be running, thus imposing a (slight) negative pressure on the tanks, which is being relieved via the vented caps. Holding a tank upside down with fuel in it prior to installation is a somewhat meaningless excersize.

    MTV
    The point of the upside down test was partly to check the cap seals, which were fine, other than the vent holes. There obviously won't be the slight negative pressure on the tank which is turned off, which may be the upwing tank, although I guess the downwing tank will also leak from the vent in the same way. I'm getting quite excited about the GoPro idea now I've thought of it

  15. #135
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    I have an 18 gallon left wing tank in my Cub and in my old Pa11. I have done 10,000 + slips and have never noticed any fuel leaking

    Glenn
    "Optimism is going after Moby Dick in a rowboat and taking the tartar sauce with you!"
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  16. #136

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    Quote Originally Posted by cubdriver2 View Post
    I have an 18 gallon left wing tank in my Cub and in my old Pa11. I have done 10,000 + slips and have never noticed any fuel leaking

    Glenn
    That’s a LOT of slips Glenn!! I think it’s leaking and coming under a wing panel somehow. I made up 2 grommets to go round the filler neck and between the tank and the tank hatch and this may be why the leak i saw is much less than it was, maybe your leak (if you have one) is running across the wing and straight out into the slipstream?


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  17. #137
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    No flaps, every landing is at least one or more slips, sometimes in ground effect to slow down. No leaks on mine. My J4 front tank is vented and when in heavy turbulence it will splash gas on the windshield, worse as tank gets emptier

    Glenn
    "Optimism is going after Moby Dick in a rowboat and taking the tartar sauce with you!"
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  18. #138

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    Quote Originally Posted by cubdriver2 View Post
    No flaps, every landing is at least one or more slips, sometimes in ground effect to slow down. No leaks on mine. My J4 front tank is vented and when in heavy turbulence it will splash gas on the windshield, worse as tank gets emptier

    Glenn
    Aha!!!! That sounds exactly what's happening with mine Glenn!!! No "leaks" but the fuel is splashing out through the vents when the wing is banked and the fuel level gets near to the cap vents!!!

    THANK YOU for that!!!

  19. #139
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    Given the long thin design of the tanks, if they’re more than half full any kind of bank angle is going to get the fuel level moving towards the cap and if it gets to the caps, what’s to stop it dribbling out of the vents as it does when the tank’s inverted?
    Not if in a coordinated turn
    Gordon

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    My SPOT: tinyurl.com/N4328M (case sensitive)
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  20. #140
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    Can you you post a photo of your caps.
    The vent hole described sounds a bit strange.[/QUOTE]

    Are these the caps you have?
    notice there are not supposed to be holes through the top as you describe. The vent path when modified is out the side.
    Fuel can not splash out of these and rain can’t get in. Less chance of fuel siphon either.
    I don’t recall any approved caps with vent holes strait through the top.

    http://rgl.faa.gov/Regulatory_and_Gu...2?OpenDocument
    Ed
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  21. #141

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    Quote Originally Posted by Gordon Misch View Post
    Not if in a coordinated turn
    True, but I'm reporting this happening in a side slip, which is probably as uncoordinated a "turn" as they come

  22. #142

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    Quote Originally Posted by cubpilot2 View Post
    Can you you post a photo of your caps.
    The vent hole described sounds a bit strange.
    Are these the caps you have?
    notice there are not supposed to be holes through the top as you describe. The vent path when modified is out the side.
    Fuel can not splash out of these and rain can’t get in. Less chance of fuel siphon either.
    I don’t recall any approved caps with vent holes strait through the top.

    http://rgl.faa.gov/Regulatory_and_Gu...2?OpenDocument[/QUOTE]

    No, they're not, they definitely have vent holes through the top and I don't recall seeing holes in the side, I'll be double checking when at the airfield this week. Thank you, we could be onto something here

    I've just looked at Univair and are these the same caps as in the AD? https://www.univair.com/atlee-dodge/...-cap-assembly/ If they are, mine are definitely different. Also, I see the vents in the cap, what's to stop fuel coming out of these vents if the wing is banked (in a sideslip) and the fuel level is above the halfway tank position and the cap is fully "submerged"?

    Is your J4 fuel cap as in the picture? and it splashes fuel out?
    Last edited by Philly5G; 10-30-2018 at 11:52 PM.

  23. #143
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    Is your J4 fuel cap as in the picture? and it splashes fuel out?[/QUOTE]

    A J-4 should be like a J-3. The nose tank has a fuel gage wire on a cork that comes up through the cap and will leak around the sleeve there. Totally different animal.
    Ed
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  24. #144

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    Quote Originally Posted by cubpilot2 View Post
    Is your J4 fuel cap as in the picture? and it splashes fuel out?
    A J-4 should be like a J-3. The nose tank has a fuel gage wire on a cork that comes up through the cap and will leak around the sleeve there. Totally different animal.[/QUOTE]

    Aha!! Thanks Ed, that makes sense!

    Update: I've been in communication with Univair and the fuel cap I posted earlier today IS to the spec of the AD and they also do the rubber grommets. I made a couple of grommets from Vitron, but mine fit the inlet pipe outer diameter exactly, whereas the Univair ones have a slightly reduced inner diameter, so they take on the coned shape the AD suggests. I'm doing the permit air test tomorrow and I'm borrowing an "official" fuel cap as per AD for the flight and will see what difference it makes....... I see an order for a couple of fuel caps, rubber grommets and 4 of the throttle friction washers (http://www.supercub.org/forum/showth...g-the-throttle) making its way to Univair in my immediate future

  25. #145
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    J4 has a fuel gauge on the dash and not on the cap.
    I modified the cap like a Luscomb cap.



    Glenn
    "Optimism is going after Moby Dick in a rowboat and taking the tartar sauce with you!"
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  26. #146
    cubpilot2's Avatar
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    Opps. I had L-4 on my brain.....
    Ed

  27. #147

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    Quote Originally Posted by cubdriver2 View Post
    J4 has a fuel gauge on the dash and not on the cap.
    I modified the cap like a Luscomb cap.



    Glenn
    Great pic! That looks like the PA-12 underwing gauges in reverse!!


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  28. #148

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    Flew today with borrowed (still not a standard Cub) fuel cap and no spills or leaks in a prolonged slip!! This is one of my 2 caps, I guess it’s time to order proper ones from Univair

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  29. #149
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    Quote Originally Posted by Philly5G View Post
    Great pic! That looks like the PA-12 underwing gauges in reverse!!


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    Bingo, I coped and built from an original

    Glenn
    "Optimism is going after Moby Dick in a rowboat and taking the tartar sauce with you!"
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  30. #150

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    Quote Originally Posted by cubdriver2 View Post
    Bingo, I coped and built from an original

    Glenn
    Great job!!!


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